Laminar near-wall combustion: Analysis of tabulated chemistry simulations by means of detailed kinetics

摘要

Chemistry pre-tabulation is well suited to include information of detailed reaction kinetics at reasonable computational costs to allow for simulations of realistic devices. In order to evaluate its accuracy in the near wall region, a study with numerical simulations of flame-wall-interaction is performed in this work. A laminar side wall -quenching scenario is considered to judge on the prediction of the global flame behavior as well as on local species formation of practical relevance. The configuration considered represents a subsection of a side-wall quenching burner introduced recently with the purpose of numerical validation in mind. The measured temperature and carbon-monoxide concentration are used to identify deficiencies of the tabulated chemistry approach. Furthermore, detailed chemistry simulations are carried out to identify the root cause for those deficiencies. The corresponding analysis is based on the transformation of the species transport equation into the composition space where the physical significance of the scalar dissipation rates provides clear indications regarding the pre-tabulation assumptions. The evaluation of individual terms allows to quantify the interaction of flamelets in the near-wall region where diffusive fluxes cause a departure from the presumed manifold. Based on this analysis, improvements are then suggested. First, as a proof of concept, the direct tabulation of the thermochemical states obtained by the detailed chemistry simulation is applied to evaluate whether the reduction to controlling variables is in general possible in such a physical scenario. Second, as an alternative way of pre tabulating, the reaction-diffusion-manifold (REDIM) approach is then adopted. By building the REDIM based on a gradient estimate from a computationally inexpensive transient one-dimensional flame-wall-interaction simulation it is possible to obtain realistic dissipation rates without a-priory knowledge. By this approximation a significant gain in prediction is achieved when compared to the original tabulation.